In view of energy saving represented by reduction in cooling load, there has been a growing tendency to make the influence of infrared rays as small as possible. With this tendency, in current years, in the field of vehicle window glass panes, for the purpose of reducing the cooling load by suppressing a temperature increase in a vehicle cabin by blocking solar radiation energy (which will be sometimes referred to insolation energy in the following) from entering into the vehicle cabin, there has been highly recommended to adopt a heat shielding glass pane that has on its outer surface an infrared reflective film for reflecting infrared.
In general, as an infrared reflective film formed on a glass pane, there are known a film (ITO film) made from a mixture of indium and tin oxide, a conductive thin film represented by a zinc oxide film to which aluminum is added, a laminated thin body having a silver film put between dielectric films, a laminated thin body having a nitride film put between dielectric films and the like.
It is general that the above-mentioned infrared reflective films are each formed on an entire surface of the window glass pane through which the infrared enters. However, since the above-mentioned conductive thin film and laminated thin bodies are able to reflect a light and a radio wave in a wide range of wavelength, the thin film and thin bodies tend to induce a radio wave interference, such as communication disturbance of portable telephones, deterioration of gain of a glass antenna provided on the vehicle window glass pane or the like, when the same are used as the infrared reflective film for the vehicle window glass pane.
In view of the above-mentioned undesired facts, one method has been proposed in which for obtaining a suitable radio wave transmissibility, the window glass pane is partially formed with radio wave transmissible areas (which will be sometimes referred to radio wave transmissible windows in the following) at portions other than those where the above-mentioned conductive thin film and the laminated thin bodies are provided (Patent Document 1).
For producing the conductive thin film and the laminated thin bodies, a vacuum film forming method such as sputtering method, CVD method (chemical vapor deposition method) or the like has been widely employed. In general, for producing the above-mentioned radio wave transmissible window in case of forming the thin film by using the vacuum film forming method, it is know to employ a masking method (Patent Document 2) in which before the film forming, a masking member, such as a metal plate, a film member or the like, is placed on a part where the radio wave transmissible window is to be produced or a wet etching method (Patent Document 3) in which part of the produced conductive thin film or part of the produced laminated thin bodies is removed with work of acid. In addition to such methods, it is also widely known to employ a method (which will be sometimes referred to dry etching method in the following) in which the produced infrared reflective film is processed or partially removed by using a grindstone (Patent Document 4), a laser (Patent Document 5), a reactive gas, radical or the like.